The invention relates generally to digital radiography and more particularly to a system and method for generating a scatter-corrected X-ray image.
The interaction of X-rays with matter is typically affected by material properties and X-ray photon energy. Compton scatter refers to the scattering effect of photons during their interaction with atoms in matter. Compton scatter results in a change in the photon energy level and causes photons to travel in different directions. The low energy scattered photons may further undergo a scattering process or a photoelectric process and the photons that arrive at the detector plane usually have low energy and do not carry any meaningful information. For traditional X-ray imaging processes, these scattered photons represent unwanted photons and are a major cause of image degradation in X-ray imaging techniques. Compton scattering also reduces the contrast of X-ray images. In particular, for applications such as quantitative radiography, where object thickness is related to the intensity of the X-ray images created without the scattered events, large errors may be encountered if the scatter component is not accurately removed.
A number of scatter reduction techniques have been proposed for minimizing the scatter effect in radiographic X-ray images. Some of these techniques include, but are not limited to, Monte-Carlo simulation, Bayesian Image Estimation, Filters, Scatter Kernel Deconvolution, Maximum Likelihood Estimation, Grid techniques, Aperture techniques and Air gap techniques. Monte-Carlo simulation uses artificial random sampling techniques to simulate and study scatter radiation effects. This technique is accurate and simple to simulate. However, it requires a high computational requirement and is time intensive. Bayesian Image Estimation is a post-processing, iterative, non-linear statistical estimation technique that reduces the scatter content while improving the contrast to noise ratio (CNR). This technique is typically used in medical imaging for scatter correction of chest images. However, it is not a generic technique for various types of objects used in industry. Metallic filters or screens may be used to reject low energy photons from the X-ray spectrum. This technique reduces some amount of scatter radiation but does not substantially improve the image quality. Grid techniques have been used successfully in the field of medical X-ray imaging. However, they have not proved to be very useful in industrial applications that have high-energy requirements for industrial inspections. Air-gap techniques reduce the field of view and introduce focal spot blurring. Aperture techniques work with reasonable accuracy but require two different exposures.
While the above techniques separate the scatter contribution from an image to produce a high contrast digital radiograph image with reasonable accuracy, they require intensive computational requirements and/or multiple and long exposures, that increase the radiation dose to a patient and decrease system throughputs. It would therefore be desirable to develop a technique that can efficiently and accurately generate a scatter-free image without the need for intensive computational requirements and multiple or long exposures.